Image forming process utilizing xerography



Feb. 18, 1969 SATORU} HONJO 3,428 453 IMAGE FORMING PROCESS UTILIZINGXEROGRAPHY Filed March 15; 1965 F 6. I F/ 6. 2

INVENTOR. SATORU HONJO A T TORNEYS United States Patent 3,428,453 IMAGEFORMING PROCESS UTILIZING XEROGRAPHY Satoru Honjo, Odawarashi,Kanagawa-ken, Japan, as-

signor to Xerox Corporation, Rochester, N.Y., a corporation of New YorkFiled Mar. 15, 1965, Ser. No. 439,764 Claims priority, applicationJapan, Mar. 19, 1964,

39/ 14,988 US. Cl. 96-1.8 7 Claims Int. Cl. G03g 7/00 ABSTRACT OF THEDISCLOSURE This invention relates to a new process of obtaining a reliefimage and more particularly to a process for obtaining a relief imagethrough the use of xerography.

There are several known processes for obtaining relief images utilizingxerography. One process uses a photosensitive xerographic layer whichcan be dissolved into suitable organic solvents and this layer isdeposited upon a photopolymerizable substrate layer as described inJapanese Patent 35 4,172. Another known process employs a xerographictoner which can change the solubility in an organic solvent of theresinous binder used in a bindertype xerographic plate layer, asdescribed in Japanese Patent 38/13,410.

There are several disadvantages to these prior processes. A xerographicbinder layer comprising finely divided, photoconductive particlesdispersed in a resinous binder generally utilizes a hydrophobic resin asthe binder so that the completed layer will have a high resistivity inthe dark. Such hydrophobic insulating resins are not soluble in water orpolar solvents but only in some of the more volatile non-polar, organic,liquid solvents. Therefore, in order to dissolve the binder layeraccording to the prior art techniques, one must employ volatile organicliquids. The use of these volatile organic liquid solvents is not onlyinjurious to the health because of the toxicity of their vapors but, inaddition, is expensive and is also dangerous because of the fire hazardwhich they create. These disadvantages would, of course, be avoided ifthe layer could be treated with water or an aqueous solution of acids,alkalis, or salts.

Xerographic layers utilizing organic photoconductive materials andalkali-soluble film-forming materials are known. However, thesematerials have much lower sensitivity to light than those containingzinc oxide and, accordingly, have very limited application.

Solubility modulation with toner materials can only be applied to thosexerographic binder layers which utilize chemically reactive resins suchas thermosetting resins.

Now, in accordance with the present invention, there has been developeda new proress of obtaining a relief divided, photoconductive particlesdissolved in a resinous binder. After the imaging process with thisphotoconductive layer has been carried out, it may be treated witheither water, volatile organic liquids or mixtures of these.Furthermore, there is no restriction imposed on the composition of thexerographic binder layer provided that the structure of the layer issuch that it permits water or other non-solvents for the layer topenetrate easily through it. The present invention utilizes axerographic plate in cluding a substrate, a suitable undercoating and axero graphic binder layer thereon. It also utilizes a specialimage-forming material which acts on the undercoating substance todecrease its solubility in water or non-polar organic liquids. Thesolubility of this underlayer is varied through the use of a tonermaterial which penetrates the xerographic binder layer according to thetreatment de scribed hereinafter to change the solubility of thatunderlayer.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings wherein:

FIG. 1 is a side sectional view of the xerographic plate utilized in thepresent invention.

FIG. 2 is a side sectional view of the same xerographic plate as shownin FIG. 1 with a xerographic toner image thereon.

FIG. 3 is a side sectional view of the same xerographic plate shown inFIGS. 1 and 2 after the toner has been caused to penetrate through thebinder layer to insolublize the undercoating.

FIG. 4 is a side sectional view of the same xerographic plate as shownin FIGS. l-3 after the xerographic layer and undercoating have beenremoved in non-image areas.

FIG. 5 is a side sectional view of a laminating process by which theplate of FIG. 1 may be prepared.

Referring now to FIG. 1, there is shown a substrate layer 1 which may beeither of electrically conductive materials such as paper, or metal,insulating materials with conductive surfaces or insulating materialswith special undercoatings. Above substrate 1 there is provided anundercoating 2 which plays an important role in the process. Thisundercoating consists of a film-forming material which has higherelectrical conductivity than the xerographic binder layer 3 above it. Inaddition, this layer is selected to be soluble in polar solvents such aswater or certain organic solvents and can be made insoluble therein bythe action of suitable chemical reagents as described hereinafter. Anysuitable material having the aforementioned characteristics may be usedfor layer 2. Typical materials having these characteristics includegelatin, casein albumin, polyvinyl alcohol, arginic 'acid, carboxymethylcellulose, polymethacrylic acid, polyacrylic acid, copolymers containingmaleic acid or maleic anhydride, copolymers containing crotonic acid,partially esterified polyamide resins, and other amide convertedpolymers containing carboxyl radicals. Metal powders or other suitablecolorants may also be compounded with these materials, When theunderlying substrate l is an insulating material, the undercoating 2 ispreferably formulated so as to have a high electrical conductivity whichmay be accomplished by mixing metal powders, carbon black particles, orgraphite particles with the film-forming materials.

The photoconductive layer 3 must have a porous or other structure suchthat it permits the penetration of liquids which can dissolvenon-converted portions of the undercoating layer 2. The xerographicplate shown in FIG. 1 can be prepared either by successive coatings orby a laminating process as shown in FIG. 5. In this latter process, aphotoconductive binder layer is prepared by ordinary coating techniqueson a temporary support layer 6 and then an adhesive layer 2 is coatedthereon. This adhesive layer has the same composition as theundercoating described above. After the preparation of this laminate, itis pressed and bonded firmly upon a final substrate 1 through theadherence of layer 2 thereto and then the temporary support layer isstripped off.

As shown in FIG. 2, a xerographic image is formed on the plate withelectroscopic developing powder 4 according to conventional xerographicimaging processes well known in the art. The particular powders employedare capable of converting the undereoating layer 2 into a form which isinsoluble in water or suitable polar solvents in which the non-convertedform of this layer is soluble. Any suitable material which will performthis function may be employed as the developing powder or as a componentthereof. Chromium-containing compounds, for example, may be used with anumber of water soluble film-forming materials in order to insolubilizethem. Typical chromium compounds of this type include: chromiumstearate, chromium naphthenate and other chromium salts of organicacids. Other polyvalent metal salts of organic acids may also be used.If these materials are solids, they may be made in the form of a powderand used by themselves as the image-forming material, If, on the otherhand, they are liquid or crystalline at room temperature,

they may be blended with suitable resinous materials which are thencrushed to form the fine developing particles thus required. Thus, forexample, a polyamide resin which is soluble in a water/methanol solventmay be rendered insoluble in this solvent by the action of one of theaforementioned acids. These acid components may be used as theimage-forming materials. Zinc chromate or lead chromate may, forexample, be utilized as imageforming materials in combination withpolyvinyl alcohol or gelatin layers. In this case, after developmentwith the chromates, the sensitive layer and the image is treated with anacid solution to dissolve the chromates which liberates the chromiumion. This chromium ion participates in a reaction with the polyvinylalcohol or gelatin layer to insolubilize it. In summary then, theimage-forming material or powder must contain a chemical component thatwill give rise to or promote an insolubilizing reaction of theundercoating when this material reaches the undercoating, or it may alsobe a promoter or catalyst for such an insolubilizing reaction of theundercoat- As shown in FIG. 3, the image forming material penetrates thephotoconductive layer 3 to reach the undercoating layer 2. Thispenetration is carried out by heating when the image is thermallyfusible or by the application of a solvent liquid or vapor to the image.If the insolubilizing reaction rate of the undercoating with the imagingmaterial is slow at room temperature, heating is effective in manyinstances to raise the reaction rate.

In FIG. 4, there is shown that stage in the process in which thephotoconductive layer and the undercoating layer has been removed innon-image areas by the action of a solvent for the unconvertedundercoating. This solvent is not a solvent for the photoconductivebinder layer. Although the solvent for the unconverted undercoatingcould not generally dissolve the photoconductive layer, experimentationhas shown that the upper photoconductive layer was easily removed bydissolving the unconverted underlayer beneath non-image areas. Among thesolvents to be used, water is one of the most desirable but mixtures ofwater and water miscible polar organic liquids are also advantageousfrom the points of view of economy, and low toxicity in work areas.

The following examples of specific compositions, structures and processsteps will serve more clearly to point out and explain preferredembodiments of the invention but it should be understood that these arenot to be construed as a limitation thereof.

Example I An aqueous solution of polyacrylic acid was coated on a steelplate and dried to produce a thickness of about 34 microns. Thefollowing composition was thoroughly mixed in a procelain ball milluntil it was well blended, coated on the polyacrylic acid layer anddried to give a thickness of about microns. The composition con- Cirsisted of parts by weight of photoconductive zinc oxide, 40 parts byweight of a low viscosity silicone resin varnish and 40 parts by weightof toluene. One plate made according to this procedure was tested byapplying water to its surface, and it was found that the surfacephotoconductive layer was porous enough so that water easily penetratedthe layer, dissolved the sub-layer thereby removing the photoconductivecoating. Testing with aqueous alkali solutions in place of the Watergave similar results. Another plate prepared according to the aboveprocedure was tested by forming a latent electrostatic image thereonaccording to conventional xerographic techniques. 'This plate was thendeveloped with a toner containing a mixture of chromium, naphthenate androsin modified phenolformaldehyde resin. After development theimage-bearing plate was heated to C. for about five minutes whereuponthe toner particles melted and penetrated into the sub-layer. Aftercooling the plate was treated with a 50/50 water-methanol solvent. Thesub-layer in non-image areas was dissolved by this treatment floatingoff the photoconductive layer above them While image areas remainedunchanged.

Example II A photoconductive coating made according to the formulationof Example I was coated on a sheet of cellophane to give a driedthickness of 10 microns. After removal of the volatile solvent amethanol solution of polyacrylic acid was coated over thephotoconductive layer to a dried thickness of 4 microns. Thispolyacrylic acid layer was then moistened with steam and the two layerswere pressed onto a steel plate with the polyacrylic acid coating facingthe steel. Subsequently, the cellophane was wet slightly and easilyseparated from the photoconductive layer leaving the tWo underlyinglayers on the steel plate. This plate was then treated according to theimaging procedure of Example I with essentially the same results.

What is claimed is:

1. An imaging member comprising a supporting substrate, a sub-layer onsaid substrate, said sub-layer being sufficiently soluble in a polarsolvent so that said sublayer can be removed from said substrate bytreatment therewith, said sub-layer comprising a material selected fromthe group consisting of gelatin casein albumin, polyvinyl alcohol,arginic acid, carboxmethyl cellulose, polymethylacrylic acid,polyacrylic acid, carboxy-group containing copolymers of organic acidsor organic acid anhydrides, carboxyl-group containing polyamides, andmixtures thereof, an upper porous insulating layer on said sub-layer,said porous insulating layer comprising finely divided photoconductiveparticles dispersed throughout an insulating hydrophobic film-formingbinder and being sufficiently porous to permit the successivepenetration of insolubilizing material and solvent material for saidsublayer through said insulating layer to said sub-layer.

2. The imaging member of claim 1 whereins said finely dividedphotoconductive particles comprise photoconductor zinc oxide.

3. An imaging member according to claim 1 in which said sub-layercomprises polyacrylic acid.

4. A method of forming a relief image comprising forming a latentelectrostatic image on an imaging member made up of a supportingsubstrate, a sub-layer on said substrate, said sub-layer being at leastpartially soluble in a polar solvent and an upper porous insulatinglayer on said sub-layer, said insulating layer being insoluble in polarsolvents, developing said latent electrostatic image with electroscopicdeveloper including an insolubilizing agent for said sub-layer and thencontacting said imaging member with a polar solvent whereby saidinsulating layer and said sub-layer are separated from said substrate innon-image areas.

5. A method according to claim 4 further including the step of causingsaid electroscopic developer to penetrate through said porous layer byapplying heat thereto prior to contacting said imaging member with saidpolar solvent.

6. A method according to claim 4 further including the step ofcontacting said electroscopic developer with a solvent vapor so as tocause it to penetrate through said porous insulating layer and contactsaid sub-layer prior to contacting said imaging member with said polarsolvent.

7. A method of forming a relief image comprising forming a latentelectrostatic image on a photoconductive imaging member by exposing saidmember to a pattern of actinic electromagnetic radiation while applyingan electrical field thereto, said imaging member being made up of asupporting substrate, a sub-layer on said substrate, said sub-layerbeing electrically conductive and at least partially soluble in a polarsolvent and an upper porous photoconductive insulating layer on saidlayer, said photoconductive insulating layer being insoluble in saidpolar solvent, developing the latent electrostatic image formed on saidimaging member with electroscopic References Cited UNITED STATES PATENTS3,121,009 2/1964 Giaimo 96-1 3,226,227 12/1965 Wolfl 96-1-8 3,236,6402/1966 Tomanek et al 96-1 3,291,738 12/1966 Sciambi 117-37 X 3,347,70210/1967 Clancy 96-1 X I. TRAVIS BROWN, Primary Examiner. C. E. VAN HORN,Assistant Examiner.

US. Cl. X.R. 96-1; 101-401.1; 117-37

